1. Field of the Invention
The present invention relates to a jack motion-restricting device for an upright piano, such as a butt and a regulating button, which restricts the motion of a jack by having the jack abut thereagainst.
2. Description of the Related Art
Conventionally, there have been proposed a butt and a regulating button for an upright piano e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H05-323953. The butt is integrally formed with a hammer, as a part of a hammer assembly, and is formed by a synthetic resin molded article. The butt has a butt felt provided on a lower end of the front surface thereof. In general, the butt felt is formed of woolen felt, and has a block shape. The regulating button is fixedly disposed on the lower surface of a regulating rail. The regulating button is formed by a cylindrical synthetic resin molded article, and has leather affixed to the lower surface thereof.
In the key-released state, a jack is held in oblique contact with the front surface of the butt felt while supporting the hammer assembly including the butt by a hammer thrust-up part, whereby the stationary position of the jack in the key-released state is defined. The regulating button in the key-released state is positioned above a base part of the jack with a predetermined space from the base part.
When a key is depressed, the associated whippen is thrust up by the key, and the associated jack is moved upward together with the whippen to thrust up the associated hammer assembly. During this process, the base part of the jack comes into abutment with the leather of the associated regulating button, whereby the motion of the jack is restricted. As a consequence, the jack is pivotally moved about the whippen, with its base part sliding on the surface of the leather, and the hammer thrust-up part is disengaged forward from the associated butt (i.e. let off). Immediately after the let-off, the hammer of the hammer assembly strikes the associated string to generate a piano tone.
Then, when the key is released, the jack moves downward together with the whippen while being pivotally moved by the associated jack spring in a direction reverse to the direction in which the jack was moved by key depression. Then, the hammer thrust-up part comes into abutment with the butt felt of the butt having performed a return pivotal motion, whereby the pivotal motion of the jack is stopped. A shock caused by abutment of the jack against the butt felt is absorbed by the butt felt, whereby generation of noise is prevented.
However, in the above-described upright piano, the butt felt is liable to expand or shrink according to changes in humidity because it is formed of wool which is a natural fiber. The stationary position of the jack in the key-released state is defined by the butt felt as described above, and hence a change in the thickness of the butt felt causes a displacement of the stationary position of the jack from a predetermined proper position. This results in changes in key touch feeling and timing for let-off or the like, which can cause a problem in touch control.
Further, since the jack strongly abuts against the butt felt whenever the key is depressed, the butt felt progressively loses its resilience due to the repeated abutment of the jack thereagainst, and finally becomes incapable of restoring from the compressed and deformed state. In such a case, the stationary position of the jack shifts in the direction of depth of the butt, which also causes changes in key touch feeling and the like. Furthermore, after coming into abutment with the butt felt, the jack, which basically performs a pivotal motion, slides on the butt felt, and hence abrasion of the butt felt occurs. Due to this abrasion, the thickness of the butt felt changes, which can cause the same inconveniences as mentioned above.
To eliminate the inconveniences, it can be envisaged that the butt felt is formed of a harder material, such as the leather used for the regulating button. In this case, however, noise is liable to occur due to abutment of the jack against the butt felt, which can cause a problem in musical performance.
As to the regulating button, since the leather is affixed to the lower surface thereof, there is also a fear that noise may be generated when the key is depressed, particularly when the key is strongly hit, thereby causing the jack to strongly abut against the regulating button. To eliminate this inconvenience, it can be envisaged that the same kind of felt as used for the butt felt is used for the regulating button in place of the leather. However, in this case, as described above, the felt expands or shrinks according to changes in humidity, and abrasion of the regulating button occurs when the jack slides on the surface of the regulating button, whereby the thickness of the regulating button is changed. This causes a displacement of the jack abutment position on the regulating button from a predetermined proper position. As a result, let-off timing changes, which can cause a problem in touch control.